Increasing evidence of sperm RNA's role in fertilization and embryonic development has provided impetus for its isolation and thorough characterization. Sperm are considered tough-to-lyse cells due to the compact condensed DNA in sperm heads. Lack of consensus among bovine sperm RNA isolation protocols introduces experimental variability in transcriptome studies. Here, we describe an optimized method for total RNA isolation from bovine sperm using the TRIzol reagent. This study critically investigated the effects of various lysis conditions on sperm RNA isolation. Sperm suspended in TRIzol were subjected to a combination of mechanical treatments (sonication and passage through a 30G needle and syringe) and chemical treatments (supplementation with reducing agents 1,4-dithiothreitol and tris(2-carboxyethyl) phosphine hydrochloride (TCEP)). Microscopic evaluation of sperm lysis confirmed preferential sperm tail versus sperm head lysis. Interestingly, only TCEP-supplemented TRIzol (both mechanical treatments) had progressive sperm head lysis and consistently yielded total sperm RNA. Furthermore, RNA integrity was confirmed based on the electrophoresis profile and an absence of genomic DNA and somatic cells (e.g., epithelial cells, spermatids, etc.) with RT-qPCR. Our findings highlighted the importance of sperm lysis, specifically of the sperm head using TCEP with mechanical treatment, in total RNA isolation and presented a bovine-specific sperm RNA isolation method to reduce experimental variabilities.
Keywords: 1,4-dithiothreitol; RNA; TRIzol; bull spermatozoa; tris(2-carboxyethyl) phosphine hydrochloride.